1. Field of the Invention
The present invention generally concerns the wireless internet, and cellular networks.
The present invention particularly concerns micromobility protocols as control the inter-cell handoff of a mobile wirelessly communicating device between stationary base stations within cells in a cellular communications network based on the Internet Protocol (IP).
2. Description of the Prior Art
2.1 General Background
By way of general background, over the past decade two unprecedented events have radically transformed the nature of modern telecommunications. The first of these is the meteoric rise and spread of the Internet, resulting in a new world wide telecommunication infrastructure based upon high speed, packet based, bandwidth upon demand as needed to support a vast array of new multimedia service offerings and applications. The second is the equally impressive emergence of cellular radio based systems which enable, in essence, wireless voice communications to small battery operated cell phones.
At the vanguard of modern telecommunications is the convergence of these two megatrends, the result of which will be a high speed, packet based wireless network capable of delivering to small handheld terminals the same grade and range of Internet based services now available only to desktop computers. Characterizing this trend are packet switching (as opposed to circuit switching), broadband(as opposed to voiceband) and on-demand bandwidth as needed to deliver multimedia content filled data files between wireless terminals and web sites.
2.2 The Particular Issue of Mobility Management in a Broadband Small-Cell Wireless Mobile Communications Network
Due to the growing demand for providing packet data services to the mobile world, future cellular networks are expected to be based on the Internet Protocol (IP). Packets will be routed up to stationary base stations using IP routers and then transmitted over the air to mobile hosts. Thus the cellular infrastructure will be an extension of the Internet.
However, the Internet was designed as a network of stationary hosts. The IP address identifies the point of attachment of the host rather than the host itself. Hence, a mobile host will need to change its IP address whenever it moved to a new base station, causing all existing connections to break down. The Mobile IP was designed to enable routing of packets to mobile hosts. See Charles Perkins, editor, “IP Mobility Support,” Internet RFC 2002, October 1996. The Mobile IP permits a mobile host to maintain a constant IP address even when it changes its point of attachment. However, while Mobile IP works well for nomadic hosts, its high latency and overhead make it unsuitable in situations requiring fast and frequent handoffs, such as might occur within a cellular network.
Thus, a hierarchical approach is needed with (i) a micromobility protocol that can manage host mobility within a large domain (intradomain mobility), and (ii) a macromobility protocol to handle mobility between domains (interdomain mobility). In other words, the global wireless infrastructure is divided into domains each of which spans an area large enough so that mobile handoffs between them are infrequent. Also, each domain is under the administrative control of a single operator. Mobility within a domain is managed by a micromobility protocol while handoffs from one domain to another are handled by the macromobility protocol. (See FIG. 1)
While Mobile IP is a natural choice for the macromobility protocol, several proposals exist for the micromobility protocol. See A. G. Valko, “Cellular IP—A New Approach to Internet Host Mobility,” ACM Computer Communication Review, January 1999; Ramachandran Ramjee, et. al., “HAWAII: A Domain-based Approach for Supporting Mobility in Wide area Wireless Networks,” International Conference on Network Protocols, ICNP'99; and Claude Castelluccia and Ludovic Bellier, “A Hierarchical Mobility Management Framework for the Internet,” IEEE Intl. Workshop on Mobile Multimedia Communications, November 1999.
It is possible that each wireless communications network operator will implement a protocol of its own choice for micromobility within its domain. If a single handset is to operate on a global level, it must be capable of detecting which micromobility protocol is used in the current domain, and then executing accordingly. A software radio based handset, with the capability to execute one of several different protocols, would be ideal for such a role. Also, if the particular micromobility protocol is not available with the handset, it should be capable of downloading the required software components over the air. Thus a single handset would be able to roam on a global scale.
The present invention concerns one possible micromobility scheme.